[Spade said:] "Eanassir, surely you cannot believe that a child at 39 days is materially different from a child of 41 days!"
I think it is about 40 days of age.
See in the following link about this subject and more details:
man-after-death.t35.com/#The_Fetus_Neither_Hears_Nor_Sees_
"Third –
A- Before 40 days of age:
[The interpreter wrote:]
"Approach to an infant, and sit near to him, on condition that his age does not exceed ten days, then shout near his head, you will see that the baby does not move or cry; for he is deaf and cannot hear any thing of your voice.
Then make another examination of this baby: that is to pass your hand in front of his eyes and you will see that he does not close his eyes and that his eyelids do not blink; that is because he is blind and cannot see anything.
Then, carefully, watch his eyes and look at his pupils, you will see that his gaze does not direct to a certain object but he is like the blind.
Then watch him when he sucks his mother's breast; he does not see the nipple in order to engulf it directly, but he will move his head left and right until it will come into his mouth, then he will engulf it.
As regards to his consciousness; the baby does not understand or realize until three months after his birth; that is because the baby, at his birth, has no hearing, sight or spiritual heart, but these form gradually; that is after the compaction of the ethereal particles from which the soul has been constructed; so that, after a short period of time: when those ethereal particles will adhere to each other, you will see that he hears, sees and becomes conscious; because, during this period, the ethereal special senses have been formed for his soul.
B- After 40 days of age:
Now do another test to confirm that:
Approach the baby with whom you did the first experiment, and sit near him, on the condition that he has exceeded forty days of age, then shout near him with a low shout; it is enough to sneeze near his head, then you will see him awake and cry because your voice has annoyed him; as if you have stricken him with a stick; for he has started to hear.
Then pass your hand in front on his eyes, and you will see him close his eyes and blink his eyelids; for he has started to see.
Then observe his pupils: you will see his gaze directing towards objects specially to the light.
Then watch him when his mother suckles him, you will see him engulf the nipple of her breast directly and does not move his head as was he doing at the beginning.
From these observations, you will realize that, during this short period of time, the hearing, sight and spiritual heart have been formed for the baby; after he was not hearing, not seeing, and after being unable to understand.
· God - be exalted - said in the Quran, 16: 78
و اللهُ أخْرَجَكُمْ مِنْ بُطُونِ أُمّهاتِكُمْ لا تَعْلَمُونَ شَيْئاً و جَعََلَ لَكُمُ السّمْعَ و الأبْصارَ و الأفْئِدَةَ لَعَلّكُمْ تَشْكُرُون .
The explanation:
(And God brought you forth [O people] from the wombs of your mothers when you knew nothing,
and He assigned for you the hearing and eye-sights and [spiritual] hearts: that you be thankful [to God.] )
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Therefore, (and He assigned for you the hearing and eye-sights and [spiritual] hearts) means: After you got out of your mothers' wombs, He made for your souls – the hearing, the sight and [spiritual] hearts; that you may thank your Lord, and show gratitude to Him.
So, the 'hearing' is the ear of the soul; the 'sight' is the eye of the soul; and the 'spiritual heart' is the heart of the soul."
man-after-death.t35.com/#The_Fetus_Neither_Hears_Nor_Sees_